The control of upright stance in young, elderly and persons with Parkinson's disease

Abstract 

The aims of the present study are twofold: (1) to compare the postural control mechanisms of young and elderly people as well as in Parkinson's disease (PD) patients during quiet standing and (2) to assess the impact of a stooped posture on these mechanisms. All subjects were required to maintain both a side-by-side and a 45° foot position. Elderly subjects performed a third condition where they were requested to mimic the stooped posture as adopted by PD subjects. The net centre of pressure (COP_net) and centre of mass (COM) profiles in the anterior/posterior (A/P) and medial/lateral (M/L) planes were analyzed. The COP_net signal was recorded from two force plates and was categorized in two mechanisms: an ankle mechanism (COP_c) and a load/unload hip mechanism (COP_v). The results showed similar postural control mechanisms in young, elderly and PD subjects. When the feet were side-by-side, the COP_net was controlled by the ankle plantar/dorsiflexors (COP_c) in the A/P direction, while by the hip abductor/adductors (COP_v) controlled in the M/L direction. When the feet were in the 45° position, both the ankle and hip mechanisms contributed to the COP_net. However, the PD subjects showed significant smaller RMS amplitudes compared to the elderly people in the 45° foot position and in the stooped posture. These findings suggest that PD subjects resort to a stiffening strategy to control their balance in postural tasks that imply a mixed control (ankle and hip mechanisms) but have adapted to their stooped posture.

Abbreviations: PD, Parkinson's disease, COM, Centre of mass, COP, Centre of pressure

Keywords: Parkinson's disease, Elderly, Postural control, Centre of pressure, Centre of mass